If you are thinking about purchasing a GPS receiver or updating the receiver you have, then you should consider the following.Waterproof:Do you need a waterproof unit? Well I certainly would because it would work in a heavy downpour or even after you dropped it in the creek - assuming you were able to retrieve it.Electronic Compass:The compass page of a non-electronic compass GPS unit works from position. It knows the direction you travel from your position. Unlike a regular compass, if you are not moving, it does not know the direction you are pointing. You must begin to move for the compass to work. If you purchase a unit with an electronic compass, then it will show direction like a regular magnetic compass except the compass can be set to show magnetic or true bearings.Two-way Radio:Some units offer a unique Position Reporting feature. This lets you send your exact location to other users in your group so that everyone can see your position on the map page. These are standard FRS/GMRS radios that you can, you can use it to communicate with any other conventional FRS/GMRS radio around. This feature could be useful for a group of guys backpacking into a remote area of the park. It offers added safety.Barometric Altimeter:If you receiver has a barometric altimeter is will pinpoint your precise elevation. All types of data becomes available. You can create elevation profiles that show your changes in elevation on a graph. These can be customized to show elevation changes in time or distance.Topographical Maps:You definitely want topographical mapping software versus or at least in addition to marine chart or autorouting software. Topographical data provides elevation contours, campground and parks information, trail data, and basic lake data. Topo software doesn't provide maps to calculate driving directions. For that, you'll need an autorouting system. If you have a boat, then you can add marine maps for this particular area.Battery Life:The length of time the unit will operate on its batteries can be very important. There are several different types of battery options depending on the particular manufacturer and model you choose. You should give this a lot of thought.Memory:All units have internal memory that can store small map segments. Better units or; higher-end units take either SD or microSD data cards for loading mapping data. All handhelds have enough memory to store waypoints and a track log without adding anything, but if you want autorouting, topo or marine software, an expandable memory system is the only way to got. Many systems even allow you to buy the maps pre-loaded onto the card that you just plug-and-play.Screen:The size of the screen is important. The larger ones are much easier to see but require that the physical size of the unit is larger. Of course you have an option of a color unit or gray scale (black and white) unit. The color units are cheap enough this day and time that this shouldn't be much of an option.The very latest are touch-screen units. This reduces the number of buttons on the unit for operation and provides more space for the display. It also makes it easier to operate the unit.My Recommendation:If you want my specific recommendation for a unit, then you certainly won't go wrong purchasing a Garmin Colorado 400t. If you would like to use satellite photos of the area that can be downloaded into the unit, weather maps and data, Satellite XM Radio and many other features, then the Bushnell Onix 400 is the best one to buy. I have one of each of the above units and use them depending on what I want that particular day. The very latest is the Garmin Oregon touchscreen unit.